Regulation of T helper cell differentiation by respiratory tract dendritic cells.

Studies on dendritic cells (DC) of the respiratory and gastric mucosae have identified an extensive network of cells that represent the predominant antigen-presenting cell type at these sites. Under steady-state conditions, respiratory tract DC (RTDC) are specialized for antigen uptake and spontaneously migrate to local lymph nodes, although in vivo transfer studies have shown that the T-cell priming activity of these cells is restricted to low-level, Th2-skewed responses. Following exposure to inflammatory stimuli, the migration of RTDC to lymph nodes is accelerated and is associated with a rapid and dramatic increase in the ability of these cells to induce both Th1- and Th2-dependent immunity. Under normal circumstances, however, responsiveness of epithelial RTDC to maturation stimuli is regulated by locally produced micro-environmental factors, including pro-inflammatory cytokines, reactive oxygen species and prostanoids. These studies have led to a greater understanding of airway DC function and their role in T helper cell differentiation and provide the basis for future studies to determine the role of the cells in the aetiology and pathogenesis of respiratory immunoinflammatory disorders.     

Folate deficiency and pancreatic acinar cell function

The present study was designed to determine the effect of folate deficiency on pancreatic acinar cell function. In the first series of experiments, three groups of rats were fed ad libitum regular rat feed, folate-deficient diet, or an equivalent amount of folate-sufficient diet. In the second series of experiments, rats were either fed ad libitum or rendered folate deficient by a purified folate-deficient diet; half of the folate-deficient group was replenished with oral folate. Body weight, pancreatic weight, DNA [methyl-14C]thymidine incorporation into DNA, RNA, [8-14C]adenine incorporation into RNA, protein content, synthesis of proteins, amylase content, and basal and bethanechol-stimulated amylase secretion were determined. The parameters were the same in the rats fed a folate-sufficient diet as in those fed a regular rat feed. Feeding a folate-deficient diet resulted in impaired DNA synthesis as evidenced by diminished incorporation of [methyl-14C]thymidine into DNA. There was no change in secretion of amylase. Similar results were obtained in the second series of experiments. These studies indicate that folate deficiency (rather than antibiotic content of the diet) impaired pancreatic function. Folate deficiency may therefore contribute to pancreatic injury in malnutrition and alcoholism.     

Activation of c-Kit in dendritic cells regulates T helper cell differentiation and allergic asthma

Dendritic cells (DCs) are integral to the differentiation of T helper cells into T helper type 1 T(H)1, T(H)2 and T(H)17 subsets. Interleukin-6 (IL-6) plays an important part in regulating these three arms of the immune response by limiting the T(H)1 response and promoting the T(H)2 and T(H)17 responses. In this study, we investigated pathways in DCs that promote IL-6 production. We show that the allergen house dust mite (HDM) or the mucosal adjuvant cholera toxin promotes cell surface expression of c-Kit and its ligand, stem cell factor (SCF), on DCs. This dual upregulation of c-Kit and SCF results in sustained signaling downstream of c-Kit, promoting IL-6 secretion. Intranasal administration of antigen into c-Kit-mutant mice or neutralization of IL-6 in cultures established from the lung-draining lymph nodes of immunized wild-type mice blunted the T(H)2 and T(H)17 responses. DCs lacking functional c-Kit or those unable to express membrane-bound SCF secreted lower amounts of IL-6 in response to HDM or cholera toxin. DCs expressing nonfunctional c-Kit were unable to induce a robust T(H)2 or T(H)17 response and elicited diminished allergic airway inflammation when adoptively transferred into mice. Expression of the Notch ligand Jagged-2, which has been associated with T(H)2 differentiation, was blunted in DCs from c-Kit-mutant mice. c-Kit upregulation was specifically induced by T(H)2- and T(H)17-skewing stimuli, as the T(H)1-inducing adjuvant, CpG oligodeoxynucleotide, did not promote either c-Kit or Jagged-2 expression. DCs generated from mice expressing a catalytically inactive form of the p110delta subunit of phosphatidylinositol-3 (PI3) kinase (p110(D910A)) secreted lower amounts of IL-6 upon stimulation with cholera toxin. Collectively, these results highlight the importance of the c-Kit-PI3 kinase-IL-6 signaling axis in DCs in regulating T cell responses.     

RAGE ligation affects T cell activation and controls T cell differentiation

The pattern recognition receptor, RAGE, has been shown to be involved in adaptive immune responses but its role on the components of these responses is not well understood. We have studied the effects of a small molecule inhibitor of RAGE and the deletion of the receptor (RAGE-/- mice) on T cell responses involved in autoimmunity and allograft rejection. Syngeneic islet graft and islet allograft rejection was reduced in NOD and B6 mice treated with TTP488, a small molecule RAGE inhibitor (p < 0.001). RAGE-/- mice with streptozotocin-induced diabetes showed delayed rejection of islet allografts compared with wild type (WT) mice (p < 0.02). This response in vivo correlated with reduced proliferative responses of RAGE-/- T cells in MLRs and in WT T cells cultured with TTP488. Overall T cell proliferation following activation with anti-CD3 and anti-CD28 mAbs were similar in RAGE-/- and WT cells, but RAGE-/- T cells did not respond to costimulation with anti-CD28 mAb. Furthermore, culture supernatants from cultures with anti-CD3 and anti-CD28 mAbs showed higher levels of IL-10, IL-5, and TNF-alpha with RAGE-/- compared with WT T cells, and WT T cells showed reduced production of IFN-gamma in the presence of TTP488, suggesting that RAGE may be important in the differentiation of T cell subjects. Indeed, by real-time PCR, we found higher levels of RAGE mRNA expression on clonal T cells activated under Th1 differentiating conditions. We conclude that activation of RAGE on T cells is involved in early events that lead to differentiation of Th1(+) T cells.     

MicroRNAs regulate dendritic cell differentiation and function

MicroRNAs (miRNAs) are an important class of cellular regulators that modulate gene expression and thereby influence cell fate and function. In the immune system, miRNAs act at checkpoints during hematopoietic development and cell subset differentiation, they modulate effector cell function, and they are implicated in the maintenance of homeostasis. Dendritic cells (DCs), the professional APCs involved in the coordination of adaptive immune responses, are also regulated by miRNAs. Some DC-relevant miRNAs, including miR-155 and miR-146a, are shared with other immune cells, whereas others have been newly identified. In this review, we summarize the current understanding of where miRNAs are active during DC development from myeloid precursors and differentiation into specialized subsets, and which miRNAs play roles in DC function.     

Cytoplasmic entry of Listeria monocytogenes enhances dendritic cell maturation and T cell differentiation and function

Protective immunity to the intracellular bacterial pathogen, Listeria monocytogenes, is mediated by a vigorous T cell response. In particular, CD8(+) cytolytic T cells provide essential effector function in the clearance of bacterial infection. The cytoplasmic entry of Listeria facilitated by listeriolysin O is an essential feature not only of the bacteria's virulence, but of the ability of the bacteria to elicit protective immunity in the host. To determine how cytoplasmic entry of Listeria regulates the development of protective immunity, we examined the effects of this process on the maturation of murine dendritic cells (DC) and on their ability to prime naive CD8(+) T cell responses. Costimulatory molecules (CD40, CD80, and CD86) were induced by listerial infection only when the bacteria invaded the cytoplasm. In addition, the production of IL-12, IL-10, IL-6, and TNF-alpha was most efficiently triggered by cytosolic Listeria. Naive T cells primed by peptide-loaded DC infected with either wild-type or nonhemolytic mutant Listeria proliferated equivalently, but a much larger proportion of those primed by wild-type Listeria monocytogenes produced IFN-gamma. Costimulatory molecules induced by cytosolic entry regulated T cell proliferation and, as a result, the number of functional T cells generated. DC-produced cytokines (specifically IL-12 and IL-10) were the major factors determining the proportion of T cells producing IFN-gamma. These data highlight the requirement for listerial cytoplasmic invasion for the optimal priming of T cell cytokine production and attest to the importance of this event to the development of protective CTL responses to this pathogen.     

滤泡辅助性T细胞分化和功能的研究进展

滤泡辅助性T细胞(Tfollicular helper cells,TFH细胞)是新近发现的一种CD4+辅助性T细胞亚群,具有不同于其他亚群的独特功能:迁移到B淋巴滤泡并辅助B淋巴细胞产生抗体。在短短的几年里面,已有大量针对滤泡辅助性T细胞分化与功能的研究。该文将对滤泡辅助性T细胞的最新研究进展作一综述。     

Vitamin D affects proliferation of a murine T helper cell clone

1,25-Dihydroxyvitamin D3 (1,25(OH)2D3), the biologically active form of vitamin D3, has been shown to inhibit the activation of T cell hybridomas and heterogeneous populations of mononuclear leukocytes. Because the response of various clones to 1,25(OH)2D3 may differ, we have examined the proliferative effects of the steroid on an antigen-specific cloned, nontransformed T helper cell line (D10.G4.1 [D10 cells]), and find that in contrast to these previous studies, the steroid is a potent stimulator of lectin-induced proliferation. In these experiments, D10 cells were incubated with concanavalin A and 1,25(OH)2D3, and although the lectin or steroid alone has minimal proliferative effects, their co-addition prompts up to a 50-fold increase in 3H-TdR incorporation at a concentration of 2.5 to 5 X 10(-9) M 1,25(OH)2D3, with significant mitogenesis occurring at 0.1 to 0.3 X 10(-9) M 1,25(OH)2D3. 25-Hydroxyvitamin D3 and 24,25(OH)2D3 have similar activity, but at concentrations two to three times greater than that of 1,25(OH)2D3, reflecting their relative affinities for the 1,25(OH)2D3 receptor. In addition, lectin treatment enhances 1,25(OH)2D3 receptor capacity fourfold to fivefold, an event coupled with the appearance of positive cooperativity. Although the steroid does not affect the quantity of bioassayable T cell growth factors as assessed by HT-2 cell proliferation, the expression of immunoreactive IL 2 receptors by lectin-activated D10 cells exposed to 1,25(OH)2D3 is enhanced. In contrast to its proliferative effect in the absence of IL 1, 1,25(OH)2D3 exerts biphasic effects on D10 replication when this monokine is present. Specifically, this steroid augments D10 proliferation at low concentrations of recombinant IL 1, but as the abundance of the monokine increases in the presence of 10(-10) to 10(-8) M 1,25(OH)2D3, the peak response of D10 cells to optimal IL 1 concentrations is diminished. Therefore, in this clone, 1,25(OH)2D3 presents itself as a regulator of T helper cell proliferation.     

The cationic antimicrobial peptide LL-37 modulates dendritic cell differentiation and dendritic cell-induced T cell polarization

Dendritic cells (DC) are instrumental in orchestrating an appropriately polarized Th cell response to pathogens. DC exhibit considerable phenotypic and functional plasticity, influenced by lineage, Ag engagement, and the environment in which they develop and mature. In this study, we identify the human cationic peptide LL-37, found in abundance at sites of inflammation, as a potent modifier of DC differentiation, bridging innate and adaptive immune responses. LL-37-derived DC displayed significantly up-regulated endocytic capacity, modified phagocytic receptor expression and function, up-regulated costimulatory molecule expression, enhanced secretion of Th-1 inducing cytokines, and promoted Th1 responses in vitro. LL-37 may be an attractive therapeutic candidate for manipulating T cell polarization by DC.     

MHC class II epitope nesting modulates dendritic cell function and improves generation of antigen-specific CD4 helper T cells

CD4 Th cells are critical to the development of coordinated immune responses to infections and tumors. Th cells are activated through interactions of the TCR with MHC class II complexed with peptide. T cell activation is dependent on the density of MHC peptide complexes as well as the duration of interaction of the TCR with APCs. In this study, we sought to determine whether MHC class II peptides could be modified with amino acid sequences that facilitated uptake and presentation with the goal of improving Th cell activation in vitro and in vivo. A model epitope derived from the murine folate receptor α, a self- and tumor Ag, was modified at its carboxyl terminus with the invariant chain-derived Ii-Key peptide and at its N terminus with a peptide that enhances uptake of Ag by APC. Modification of a peptide resulted in enhanced generation of high-avidity murine folate receptor α T cells that persisted in vivo and homed to sites of Ag deposition. The nesting approach was epitope and species independent and specifically excluded expansion of CD4 regulatory T cells. The resulting Th cells were therapeutic, enhanced in vivo helper activity and had an increased ability to resist tolerizing immune microenvironments. In addition to improved immunoadjuvants, this epitope modification strategy may be useful for enhancing ex vivo and in vivo generation of Th cells for preventing and treating diseases.     

Propagation of antigen-specific T cell helper function in vitro.

Antigen-induced proliferation of primed lymph node cells was abrogated by treatment with anti-Ly 1 serum and complement (C) but not with anti-Ly 2 serum and C. Lymph node cells from animals primed to ovalbumin were activated with antigen in vitro, followed by propagation in an antigen-free supernatant fluid obtained from lectin-induced normal spleen cells. T cells processed in this manner displayed a stepwise enrichment of helper activity for antibody production as measured in a secondary hapten-carrier response. The sequential increase in antigen-specific help was paralleled by a rise in the antigen-induced proliferative response, a phenomenon whose expression was dependent on the presence of syngeneic or semi-syngeneic irradiated filler cells.